guix-config: Keep build deps with "guix gc"

.guix-config/config.scm

@@ -119,20 +119,26 @@
 ;; log-in service, networking with Wicd, and more.
 (define %my-services
   (modify-services
-   %desktop-services
-   (udev-service-type config =>
-                      (udev-configuration
-                       (inherit config)
-                       (rules (append (udev-configuration-rules config)
-                                      (list ;; %nitrokey-udev-rule
-                                       %backlight-udev-rule)))))
-   (slim-service-type config =>
-                      (slim-configuration
-                       (inherit config)
-                       (auto-login? #f)
-                       (startx (xorg-start-command #:modules my-xorg-modules))
-                       ;; TODO: Can't slim pre-fill the username?
-                       (default-user "ambrevar")))))
+      %desktop-services
+    (guix-service-type config =>
+                       (guix-configuration
+                        (inherit config)
+                        ;; Don't clean build deps.
+                        ;; See (info "(guix) Invoking guix-daemon").
+                        (extra-options '("--gc-keep-outputs"))))
+    (udev-service-type config =>
+                       (udev-configuration
+                        (inherit config)
+                        (rules (append (udev-configuration-rules config)
+                                       (list ;; %nitrokey-udev-rule
+                                        %backlight-udev-rule)))))
+    (slim-service-type config =>
+                       (slim-configuration
+                        (inherit config)
+                        (auto-login? #f)
+                        (startx (xorg-start-command #:modules my-xorg-modules))
+                        ;; TODO: Can't slim pre-fill the username?
+                        (default-user "ambrevar")))))
 
 (operating-system
  (host-name "mimimi")